In a projector, printer, or another image forming device, to improve the resolution of the image, there is known the method of scanning by light rays from a one-dimensional image display element by a scan mirror or other optical scanning device while projecting images onto an image forming means to form a twodimensional image (for example, refer to U.S. Pat. No. 5,982,553).
As a one-dimensional pixel display device, a Grating Light Valve™ (GLV) developed by Silicon Light Machines of the U.S. is known (for example, Japanese Examined Patent Publication (Kokoku) No. 3164824 and U.S. Pat. No. 5,841,579).
In comparison with the usual two-dimensional display device, when using a GLV, while the number of pixels in the vertical direction becomes the same, just one is sufficient in the horizontal direction, so the number of pixels required for the two-dimensional image display is smaller. Further, the electrode portions, referred to as “ribbon elements”, of the GLV are very small in size (about 1×40 μm), therefore a high resolution, a high switching speed, and a display of a wide bandwidth are possible. On the other hand, a low application voltage is used for the operation, so realization of very small sized display devices can be expected.
Referring to FIG. 1 to FIG. 3, the general configuration of an image display device using a GLV will be simply explained.
FIG. 1 is a view of an example of the configuration of an image display device using a GLV.
An image display device 100 shown in FIG. 1 has a screen 101, a scan mirror 102, a scanner motor 103, a projection optical system 104, a one-dimensional light modulation element 105 formed by a GLV device, a drive circuit 106 for supplying a drive voltage to the GLV device 105, an interface circuit 107, a video data conversion circuit 108, a scanner driver 109, and a system control circuit SYS-CNT 110. The configuration including the scan mirror 102 and the scanner motor 103 will be referred to as a “scanner 102a”. 
For example, a light source LS comprising a plurality of semiconductor lasers emits red (R), green (G), or blue (B) illumination light rays. The illumination light rays are converted to parallel beams by a not illustrated illumination optical system and irradiated to the GLV device 105.
The GLV 105 is formed by a plurality of pixels arrayed one-dimensionally. A drive voltage in accordance with the image to be displayed is supplied to the GLV device 105 by the drive circuit 106. The GLV device 105 reflects or diffracts the incident illumination light in response to this and emits the reflected light or the diffracted light to the projection optical system 104.
The projection optical system 104 converts the reflected light or the diffracted light emitted from the GLV device 105 to parallel beams. Further, the projection optical system 104 separates the ±1st order diffracted light and 0 order light, passes the ±1st order diffracted light to make it reach the scan mirror 102, and blocks the 0 order light. Further, the projection optical system 104 enlarges mainly the one-dimensional image formed by the ±1st order diffracted light from the GLV device 105 and projects and focuses it onto the screen 101 via the scan mirror 102.
The scanner motor 103 is driven by a scanner drive signal SDS from the scanner driver 109 and reciprocally rotates the linking scan mirror 102. The scan mirror 102 scans by ±1st order diffracted light including the one-dimensional image emitted from the projection optical system 104 and sequentially emits it to the screen 101 while reciprocally rotating to form a two-dimensional image. The scan mirror 102 is for example a galvano mirror.
The video data VD input to the image display device 100 is for example a color difference signal YCbCr (YPbPr) input from a DVD or other video player. In order to process it at the image display device 100, the video data conversion circuit 108 and the interface circuit 107 convert the format of the input video data and output it to the drive circuit 106 for every one-dimensional image (referred to as “one line”).
The system control circuit SYS-CNT 110 has a CPU 111 and a memory 112 and distributes a frame synchronization signal FRMsync for synchronizing the components of the image display device 100. Further, it outputs basic data for driving the scan mirror 102 and a scanner instruction signal SIS including a phase, an amplitude, and cycle information for the data. Further, it generates a modulation/projection signal RQT indicating the modulation and projection timings of the GLV device 105 using various types of data.
FIG. 2A is a view schematically explaining a scanning operation of the scan mirror 102, while FIG. 2B shows a two-dimensional image formed on the screen 101 by the scanning of the scan mirror 102.
As shown in FIG. 2A, the scan mirror 102 sequentially irradiates the one-dimensional image light projected from the projection optical system 104 to the screen 101 while reciprocally rotating within a predetermined angle range so as to form a two-dimensional image on the screen 101.
The scanner 102a (scan mirror 102 and scanner motor 103) is driven by a saw-tooth wave-like signal shown in FIG. 3.
As shown in FIG. 3, when driving the scanner 102a by a saw-tooth wave-like signal having an asymmetric rising characteristic (time and amplitude) and falling characteristic (time and amplitude) and exhibiting a saw-tooth like shape, an illustrated drive voltage is supplied to the scanner 102a and the scanner 102a is driven in the periods T1a and T1. In the period T1a, the scan mirror 102 has a rotational speed accelerated from zero to a predetermined speed. In the period T1, the scan mirror 102 rotates at a constant speed from a position “a” to a position “c” while passing a position “b” along an outgoing direction shown in FIG. 2A, reflects the incident one-dimensional image light at each position, emits light rays La, Lb, and Lc to the screen 101, and forms the one-dimensional images Sa, Sb, and Sc shown in FIG. 2B.
In the period T1 shown in FIG. 3, the scan mirror 102 rotates up to the position c.
Thereafter, in the period T2 shown in FIG. 3, the scan mirror 102 decelerates until the rotational speed becomes zero and starts to rotate in reverse while accelerating along a return direction shown in FIG. 2A.
In the period T2, the scan mirror 102 rotates in the return direction, but in the T2 period, the scan mirror 102 only returns to its original position for the next projection and does not project or focus the image.
As described above, when projecting an image by scanning in accordance with a saw-tooth wave-like signal, the image is projected for only the T1 period and is not projected in a movement time T2 in the return direction, so a useless time T2 was generated. Therefore, the light projection efficiency of the scanner 102a was low. When trying to raise the light projection efficiency of the scanner 102a, there is the method of shortening the movement time T2 in the return direction, but a large power must be supplied to the scan mirror 102 in order to return the scan mirror 102 in a short time. For this reason, there was the problem that there was a demand for increasing the amount of the electric power of the scanning device and for raising the mechanical strength of the scan mirror. The scanning device became large in size and expensive to realize this.